Selectively hydrogenated block copolymers

ABSTRACT

Block polymers are provided having substantially improved capability of forming stable elastomeric polar derivatives, these block polymers being prepared by block polymerizing a monovinyl arene with butadiene, the butadiene block containing between about 8 and about 80 percent 1,2-structure and thereafter selectively hydrogenating so as to substantially eliminate the unsaturation in the pendant vinyl groups.

United States Patent Winkler 1 Oct. 24, 1972 [54] SELECTIVELYHYDROGENATED 3,526,606 9/1970 Minekawa et al. ..260/5 BLOCK COPOLYMERSPrimary Examiner-James A. Seidleck De Loss [72] lnvmor E wmkler OnndaCahf Assistant Examiner-Richard A. Galther Asslgnee! p y New York,Attorney-Joseph W. Brown and William H. Myers [22] Filed: May 22, 1970ABSTRACT [21] Appl. No.: 39,919

Block polymers are provided having substantially improved capability offorming stable elastomeric polar [52] US. Cl. ..260/879, 260/880 Bderivatives these block polymers being prepared by [51] Int. Cl.f ..C08f19/08, C08f 27/24 block polymerizing a monovinyl arene with butadiene,Fleld 0 B the butadiene block containing between about 8 and about 80percent 1,2-structure and thereafter selec- [56] References and tivelyhydrogenating so as to substantially eliminate UNITED STATES PATENTS theunsaturation in the pendant vinyl groups.

3,431,323 3/1969 Jones ..260/880 8 Claims, No Drawings SELECTIVELY HYDROGENATED BLOCK COPOLYMERS This invention is concerned with theproduction of block copolymers. More particularly, it is directed to thepreparation of selectively hydrogenated block copolymers especiallyuseful for further derivatization.

The art of block copolymer formation has developed rapidly in the pastfew years, with the result that a number of block copolymer types havebeen proposed. These block copolymers may have two or more polymerblocks and may be either essentially linear or branched in at least partof the entire molecule. They may be prepared by a variety of processesone of which involves sequential addition of the individual monomers toform the individual polymer blocks or a combination of sequentialaddition and coupling may be employed. The choice of the coupling agenthas been found to be important in creating the desired structure, i.e.,linear or non-linear products. Furthermore, the art has been directed inpart to the production of derivatives of these block polymers so as tomodify them with polar radicals. Also, hydrogenation has been utilizedto improve their oxidative stability and alter their servicetemperatures. The set of physical characteristics may be tailor made bychoosing the alternatives listed above as well as by controlling theindividual block molecular weights as well as the ratio of the differentspecies of blocks. For example, when rubbery products are desired, it ispreferred to utilize as one of the monomers a conjugated diene which isthen utilized to form a predominating amount on a weight basis of thepolymer blocks. On the other hand, if thermoplastic non-rubbery productsare required, a monomer normally capable of forming a thermoplasticresin is employed as the predominating monomer such as styrene or alphamethyl styrene.

In the usual formation of a block copolymer according to the prior art,it has been found that a simple structure such as A-B-A wherein each Ais a monovinyl arene polymer block and B is a conjugated diene polymerblock will have so-called thermoplastic elastomeric properties if theentire polymer contains less than about 55 weight percent of the A typeblocks. These are usually prepared by the use of a lithiumbasedcatalyst, preferably a lithium alkyl. It is known that this produces inthe conjugated diene block a mixture of several types of structureswhich in the art are referred to as cis l,4-, trans 1,4-, and1,2-structures. These refer to the way in which the diene units areattached to one another. In the cis and trans 1,4 varieties, the carbonatom arrangement is all in line with no carbon atoms pendant from thebackbone carbon atom chain. When 1,2-structures are present, thestructure is such that pendant vinyl groups are present, these beingdirectly attached to the two remaining carbon atoms of the diene monomerunit to which they were originally attached. Unless great care is taken,the normal diene polymerization will result in all three types beingpresent in a polymer block. However, means may be utilized as known inthe art for maximizing any one of these types if so desired.

As stated hereinbefore, one of the avenues 'of development in blockpolymers has been the formation of a variety of derivatives thereofwherein the derivatization has resulted in the combination of polargroups at various points in the polymer chain. A

number of reactions are known for this purpose, includinghydrohalogenation, halogenation, carboxylation, epoxidation,hydroxylation, chlorosulfonation, and other derivative processes. Thepolar derivatives so formed may be useful for a number of commercialpurposes but up to the present time a major obstacle has limited theiruse. This is that in most cases where an effective proportion of polargroups have been formed on the block polymer chain the resultingproducts are nonelastomeric and have lost their formerly desirable setof physical properties. This apparently is due to the cyclization whichmay occur during derivatization on the pendant vinyl double bonds, andthe formation of unstable polar groups on tertiary carbon atoms presentin the backbone carbon chain. This allows ready decomposition of theproduct and loss of elastomeric properties to such a degree that theproducts have relatively little commercial utility.

It is an object of the present invention to provide improved blockcopolymers. It is a particular object of the invention to provide aprocess for the production of such copolymers. It is a special object ofthe invention to provide block copolymers capable of forming improvedblock copolymer derivatives. Other objects will become apparent duringthe following detailed description of the invention.

Now, in accordance with the present invention, a block copolymer isprovided satisfying the above objects which comprises a partiallyhydrogenated block copolymer having, prior to hydrogenation, at leastone monovinyl arene polymer block and at least one polybutadiene blockwherein the polybutadiene block has between about 8 and about percentl,2-structure showing infrared absorbance at 10.98 microns and 10.05microns, the balance of the polybutadiene block being 1,4-structured,said block copolymer being selectively hydrogenated so as to removesubstantially all unsaturation in the pendant vinyl groups and no morethan about 50 percent of the unsaturation in the 1,4- structuredportions of the block. In accordance with the present invention, it hasbeen found that such selectively hydrogenated block copolymers areespecially promising precursors useful for the formation of polarderivatives. They are moreover useful as polymers without furtherderivatization if so desired. The substantial elimination ofunsaturation in the pendant vinyl groups which are inherent in the1,2-structure portion of the butadiene block virtually eliminates thepossibility of any addition reactions taking place on these pendantgroups. Therefore, any derivatization such as, for example,hydrohalogenation, occurs only on carbon atoms forming a part of thebackbone carbon chain. This results in a product which does not tend tocyclize during later derivatization steps. Moreover, since butadiene isthe diene employed in the polymers of the present invention, no tertiarycarbon atoms are present in the backbone carbon chain as would bepresent in a similar polyisoprene polymer block. Consequently, anygroups which are attached to the backbone carbon atoms are attached onlyto secondary carbon atoms and moreover are'spaced apart from one anotherby a minimum of four carbon atoms. l

The preparation of the precursor block copolymer may follow processesbroadly known in the block polymer art. In general, the products willhave the general formula A-B(-B-A) According to this formula, each A,prior to hydrogenation represents a monovinyl arene block and each Brepresents a polybutadiene block. Where at any point two essentiallyidentical blocks B are directly connected (except for any residue of acoupling agent), the connected blocks are considered to be a singleblock for the purpose of describing block molecular weights, etc. Thus,this general formula includes the following types: Where the subscriptis 0, a two-block copolymer results having the structure A-B. Where thesubscript is l, the resulting structure is A--B-A, which is a linearblock copolymer structure. Branched structures are obtained when thesubscript is between 2 and 5. For example, where a tetrafunctionalcoupling agent is employed, the structure will be represented asfollows:

to be represented by: A-lil-B-A The monovinyl arene polymer blocks A areprepared from such monomers or mixtures thereof as styrene, alpha methylstyrene, ring alkylated styrenes and the like. Styrene and alpha methylstyrene are preferred species, These may be modified by minorproportions based on the proportion of monovinyl arene ofcopolymerizable monomers such as conjugated dienes, vinyl pyridines andthe like. Solution polymerization is preferred and for this purposelithium-based catalysts are utilized which may be either monofunctional,e.g., lithium alkyls or polyfunctional, e.g., dilithionaphthalene.

The monomers are dispersed in suitable inert solvents such as alkenes,alkanes, cycloalkenes or cycloalkanes such as butenes, pentenes,butanes, pentanes, cyclopentene, cyclopentane or cyclohexane, as well astheir mixtures. Anaerobic conditions are essential and a high state ofpurification of the monomers and solvents also is highly desirable ifnot essential. This may be achieved by scavenging any reactiveimpurities with carefully introduced portions of a polymerizationinitiator prior to introduction of the main body of the initiator forthe purpose of polymerizing the desired monomer. As a simpleillustration, styrene is introduced into cyclohexane and impurities arescavenged therefrom by the introduction of small 5 amounts of a lithiumalkyl such as lithium secondary butyl to the point of incipientpolymerization. At this point, a sufficient amount of lithium alkyl isadded to initiate polymerization and form a polymer block of styrene ofpredetermined molecular weight, said block being associated at one endwith a lithium ion. 'Thereafter, butadiene is injected into the system Ipreferably previously scavenged with lithium secondary butyl to removeany undesired impurities. The butadiene block polymerizes with theliving polystyrene block, polymerization being carried to apredetermined extent to form a polybutadiene block having a desiredaverage molecular weight. The associated lithium ions may be removed orneutralized by the addition of polar materials such as an alcohol,water, or oxygen.

The linear three-block polymer A-B-A may be formed by a second additionof monovinyl arene monomer such as styrene to the living polymer blockA-B-Li and continuing polymerization until the A-B structure iscompleted. Alternatively, the intermediate living block copolymer A-B-Liis formed in such a way that the average molecular weight of B is onlyabout one-half that desired in the final polymer. At this point, adifunctional coupling agent such as a dihaloalkane may be added to thereaction mixture to form the dicoupled product A -(-B-B)-A.

If star-shaped, radial, branched, or non-linear (depending on thenomenclature preferred) are desired, the intermediate block copolymerA-B-Li is first synthesized and thereafter a polyfunctional couplingagent is injected into the living polymer system to form a branchedcoupled product as indicated in the general formulas above. Suitablecoupling agents of this type include silicon polyhalides such as silicontetrachloride, diesters of dicarboxylic acids with monohydric alcohols,such as diethyl adipate and other polyfunctional coupling agents knownin this art.

While molecular weights are not a limiting feature of the presentinvention, the blocks A usually have average molecular weights of2,000-50,000 and the blocks B have average molecular weights of10,000-25 0,000, as determined by tritium counting methods.

In all of the above typical reactions, means must be taken to achievethe degree of l,2-structure desired in the polybutadiene block. This isreadily controlled by including in the reaction mixture at least duringthe formation of the polybutadiene block a polar material such as anether, thioether or a secondary amine. Typical of these are diethylether, tetrahydrofuran or diethyl amine. The l,2-structure in thepolybutadiene block should be between about 8 and about 80 percent asdetermined by infrared analysis.

The block copolymer prepared by this or equivalent processes and havingthe recited proportion of 1,2- structure in the polybutadiene block(s)is now in condition for selective hydrogenation to prepare the desiredpartially hydrogenated products. The objective in this hydrogenationstep is to substantially completely hydrogenate the unsaturated linkagespresent in the pendant vinyl groups which are the result of the 1,2-structure formation, while at the same time hydrogenating no more than50 percent of the unsaturated bonds which lie in the backbone carbonchain. Preferably, less than about 25 percent of the backbone doublebonds are hydrogenated, the objective being to eliminate those doublebonds which lie in areas, e.g., pendant vinyl groups resulting inundesirable cyclization while at the same time leaving exposed doublebonds in the backbone carbon chain Where derivatization is highlydesirable.

Hydrogenation is preferably carried out in solution in an inerthydrocarbon, preferably the same hydrocarbon solvent employed duringpolymerization. Polymerization catalysts comprise preferably, but notexclusively, the cobalt, nickel, or iron carboxylates or alkoxidesincluding acetyl-acetonates of Ni or Ca reduced with an aluminum alkylcompound. Hydrogenation conditions are selected to mildly hydrogenate,the vinyl unsaturation being the first to become saturated.Consequently, the preferred hydrogenation pressures are between about 1atmosphere and about 1,500 psig partial pressure of hydrogen, preferably100-1200 psig. The hydrogenation temperatures are preferably betweenabout 25 and about 100C. The time of hydrogenation under such conditionswill normally be between about 0.1 and about 2 hours.

The monovinyl arene blocks ordinarily will not be hydrogenated to anyappreciable extent under these mild selective hydrogenation conditionssince it has been found that substantially all of the aliphatic doublebonds will be hydrogenated prior to any appreciable amount of aromaticdouble bond saturation.

The product resulting from this selective hydrogenation may be examinedby infrared analysis to determine the presence or absence of any vinylgroups. In the usual infrared analysis, any trans structure will showstrong absorbance at 10.35 microns, while any cis structures will showabsorbance at 13.60 microns. The 1,2-structure shows absorbance attwo-wave lengths, namely, 10.98 and 10.05 microns. It is desirable inthe final product that substantially no absorbance in these lattertwo-wave lengths be observed in the selectively hydrogenated product.The products of the present invention will be found to have asubstantially reduced iodine number from that of the original material.This will depend in part upon the proportion of the conjugated dienepolymer block(s) in the starting products. However, in the product ofmost commercial utility, the iodine number prior to selectivehydrogenation will be in the order of 200-400, while the selectivelyhydrogenated products will usually have an iodine number in the order of50-150 grams iodine added per 100 g of polymer.

The following working example illustrates the preparation of theprecursor block copolymer, the selective hydrogenation thereof, and thephysical properties of the latter product.

EXAMPLE 1 Preparation of Block Copolymer All monomers and solvents weretreated to remove water, oxygen, and polar materials and thepolymerization was done under a nitrogen blanket.

There was charged to a reactor 4,200 g of cyclohexane and 468 g ofstyrene. Any impurities were titrated with sec-butyllithium and then0.031 moles of sec-butyllithium in 275 g solution in cyclohexane wasadded and the polymerization was run for 1 hour at 50C to convertessentially all of the styrene monomers. A sample 132 g) of solution waswithdrawn for analysis.

The above living polymer solution was transferred to a second reactorwhich contained 2,160 g of butadiene, 11,535 g of cyclohexane and 50 gof THF (THF/Li= pretitrated with sec-BuLi. The butadiene was essentiallyall consumed after 3 hours at 40. Removed sample for analysis. (Tl-1F istetrahydrofuran.)

There was then added a pretitrated solution of 442 g of styrene in 2,650g of cyclohexane. After 1 hour at 45, the polymerization was complete. Athird sample was removed for analysis. Block lengths were found to be13,000-68,00015,000 by a tritium method, and the butadiene block had 46percent 1,2-structure.

Partial Hydrogenation of the Block Copolymer The polymer solution fromthe above preparation was charged to a hydrogenation autoclave. For

catalyst, 6 mmoles of Ni acetylacetonate [Ni(C l-1 O aplus 12 mmoles oftriethyl aluminum reacted for 15 minutes at 25C in 1,500 mole ofcyclohexane were added. The autoclave was pressured to 500 psig withhydrogen. The temperature rose to 50C. After 25 minutes, the polymer hadan iodinenumber of 81 and was suitable for derivatization.

Pertinent physical properties were as follows:

Tensile strength at break, psi 7000 300% Modulus, psi 650 Eldhgation atbreak, 590 Set at break, 20

1 claim as my invention:

1. A partially hydrogenated block copolymer having at least onemonovinyl arene polymer block and at least one polybutadiene blockwherein the polybutadiene block has between about 8 and about percent1,2- structure showing infrared absorbance at 10.98 microns and 10.05microns, the balance being 1,4- structure, said block copolymer beingselectively hydrogenated so as to remove substantially all unsaturationin the pendant vinyl groups and no more than about 50 percent of theunsaturation in the 1,4-structured portions of the block, said partiallyhydrogenated block copolymer having an iodine number between 50 and 150.

2. A partially hydrogenated block copolymer according to claim 1 showingsubstantially no absorbance at 10.98 and 10.05 microns.

3. A partially hydrogenated block copolymer according to claim 1 havingthe structure prior to hydrogenation of wherein A is a monovinyl arenepolymer block and B is a butadiene polymer block.

4. A partially hydrogenated block copolymer according to claim 1 havingthe general structure prior to hydrogenation of wherein A is a monovinylarenepolymer block and B is a butadiene polymer block.

5. A partially hydrogenated block copolymer according to claim 1 havingthe general structure prior to hydrogenation of An -Am wherein A is amonovinyl arene polymer block and B is a butadiene polymer block.

6. A partially hydrogenated block copolymer according to claim 1 havingthe general structure prior to hydrogenation of

2. A partially hydrogenated block copolymer according to claim 1 showingsubstantially no absorbance at 10.98 and 10.05 microns.
 3. A partiallyhydrogenated block copolymer according to claim 1 having the structureprior to hydrogenation of A-B wherein A is a monovinyl arene polymerblock and B is a butadiene polymer block.
 4. A partially hydrogenatedblock copolymer according to claim 1 having the general structure priorto hydrogenation of A-B-A wherein A is a monovinyl arene polymer blockand B is a butadiene polymer block.
 5. A partially hydrogenated blockcopolymer according to claim 1 having the general structure prior tohydrogenation of A B-A1 5 wherein A is a monovinyl arene polymer blockand B is a butadiene polymer block.
 6. A partially hydrogenated blockcopolymer according to claim 1 having the general structure prior tohydrogenation of A-B B-A1 5 wherein A is a monovinyl arene polymer blockand B is a butadiene polymer block.
 7. A partially hydrogenated blockcopolymer according to claim 6 wherein A is a poly(alpha methyl styrene)block.
 8. A partially hydrogenated block copolymer according to claim 4having the general structure, prior to hydrogenationpolystyrene-polybutadiene-polystyrene.